全文获取类型
收费全文 | 472篇 |
免费 | 23篇 |
国内免费 | 81篇 |
专业分类
化学 | 353篇 |
晶体学 | 2篇 |
力学 | 54篇 |
综合类 | 5篇 |
数学 | 7篇 |
物理学 | 155篇 |
出版年
2023年 | 1篇 |
2022年 | 13篇 |
2021年 | 19篇 |
2020年 | 13篇 |
2019年 | 11篇 |
2018年 | 16篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 27篇 |
2012年 | 35篇 |
2011年 | 25篇 |
2010年 | 28篇 |
2009年 | 28篇 |
2008年 | 22篇 |
2007年 | 39篇 |
2006年 | 35篇 |
2005年 | 30篇 |
2004年 | 27篇 |
2003年 | 22篇 |
2002年 | 13篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 13篇 |
1997年 | 16篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 1篇 |
排序方式: 共有576条查询结果,搜索用时 0 毫秒
171.
172.
173.
174.
175.
大型汽轮机部件低周疲劳安全寿命的设计和评定 总被引:1,自引:0,他引:1
文中提出了汽轮机部件低周疲劳安全寿命的设计和评定方法。介绍了汽轮机部件低周疲劳安全寿命的含义和计算方法。该方法以概率论和统计学为基础,把汽轮机部件的低周疲劳寿命处理为随机变量,对低周疲劳试验数据进行统计分析来确定材料低周疲劳寿命的分布参数,使用可靠性理论来确定汽轮机部件的低周疲劳安全寿命。文中给出了低周疲劳寿命服从正态分布和对数正态分布时汽轮机部件低周疲劳安全寿命的计算方法和应用实例。该方法考虑了汽轮机运行参数随机性和材料低周疲劳特性离散性的影响,为汽轮机部件低周疲劳寿命的设计、评定和诊断提供了科学的依据。 相似文献
176.
Jean Piquemal 《Transport in Porous Media》1994,17(2):105-120
This paper presents a method and describes an experimental device for determining the steam-water relative permeabilites of unconsolidated porous media. The experimental conditions are as close as possible to those of geothermal reservoirs. The relative permeabilities have been obtained at 180 and 150?C. Their variations versus liquid saturation are quite classical. The air-water relative permeabilities have been measured also at room temperature. The values obtained under these three conditions are almost identical. However, the air-water relative permeability differs slightly from that of steam at 180 and 150?C. We think this discrepancy is acceptable in practice, as it is easier to determine the relative permeabilities for an air-water flow at room temperature than for a steam-water flow at high temperature and pressure. 相似文献
177.
Conventional compression-refrigeration systems not only consume a large amount of electric power, but also cause serious environmental pollution. Among the various possible approaches in overcoming these two problems, a steam-ejector refrigeration system is believed to be most effective. This paper experimentally investigates the controlling parameters of a steam ejector, including operating conditions and the exit Mach number of the primary nozzle. Operation maps useful to the practical design are constructed from experimental results, and the empirical equations are correspondingly derived. Excessively increasing the exit Mach number of primary nozzle is unnecessary, and 4.35 should be a moderate value. With regard to the performance characteristics of the ejector itself, a steam ejector is better than an R114 ejector and is comparable to an R113 ejector. Moreover, with the use of a two-stage ejector, the required pressure to drive a steam ejector is reduced, and the low-grade heat source can be efficiently used. The results of primitive observation of the flow field are also discussed in this work. 相似文献
178.
A convenient experimental method for measuring the thermal conductivity of uranin (fluorecein sodium, C20H10O5Na2) is described. Two similar blocks of uranin, produced from a strong uranin/water solution, were exposed to one-dimensional steady-state conduction. It was found that, for a mean bulk temperature ranging from ambient up to 55°C, the uranin has a constant thermal conductivity of 0.43 W/mK. Above these temperatures, the material begins to soften and the thermal conductivity is seen to decrease 相似文献
179.
The plane one-dimensional and radially symmetric problems of injection of superheated steam into a porous medium saturated with gas are considered. Self-similar solutions are constructed on the assumption that in this case four zones are formed in the porous medium, namely, a gas flow zone, superheated and wet steam zones, and a water slug zone formed due to steam condensation. On the basis of the solution obtained, both the effects of the boundary pressure, mass flow rate, and temperature of the injected superheated steam and the effect of the initial state of the porous medium on the propagation of the hydrodynamic and thermal fields in the porous medium are studied. 相似文献
180.
We formulate conservation laws governing steam and nitrogen injection in a one-dimensional porous medium containing water.
Compressibility, heat conductivity and capillarity are neglected. We study the condensation front and shock waves arising
in the flow. We find that there are four possible types of solutions for the initial and boundary conditions of interest.
We describe a simple construction in the temperature saturation plane that determines the complete solution for the given
conditions. Applications of the theory developed here are in clean up of soil contaminated with nonaqueous phase liquids.
We show that a substantial cold gaseous zone develops in all solutions of practical interest, thus counteracting downward
migration of the pollutant. 相似文献